AirPrint is entirely reliant upon multicast network traffic being reliably passed throughout the WiFi network. As described, the WiFi network device architecture (with the Printer reliant upon a WiFi repeater) cannot reliably pass Apple Bonjour (mDNS) traffic. As such AirPrint Printer discovery is failing - most likely due to ARP and/or DHCP timeout. The Apple Bonjour protocol uses mDNS (Multicast DNS) UDP port 5353.
A restart of your network components may temporarily resolve the problem. You’ll need to restart your network devices in the correct order. Assuming that you WiFi Router provides DHCP and DNS services for your network, restart devices in this order - allowing time for devices to fully boot/restart prior to restarting other devices:
- WiFi Router
- Wired Network Switch(es)
- WiFi Access Points / Network Extenders
- Other fixed infrastructure devices - such as Printers
- Client devices
Restarting your iPad, after restarting other devices in the correct sequence, is most simply achieved by a forced-restart of the iPad:
- On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
- On an iPad with Face ID: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.
As already stated, this may only provide temporary relief. You would be best advised to move the printer closer to the WiFi Router such that the Printer is not reliant upon the WiFi Repeater - but instead connects to the central WiFi router.
If set-up correctly, should you continue to experience difficulties, your WiFi Router may be unexpectedly failing to pass Apple Bonjour traffic on you local network - or your WiFi Router or Network Switch may be dropping this device discovery protocol.
If you continue to have difficulties, check to see if your iPad is using the new WiFi Private Address feature. This feature is intended to provide additional privacy and security when using “public” (untrusted) WiFi networks.
Settings > WiFi > [Your WiFi Network / SSID] - tap the “i” icon - Private Address
The Private Address feature is largely unnecessary for your home WiFi network; if enabled, Private Addressing can interfere with anticipated operation of other devices, such as AirPrint. In such circumstances, you may need to disable this feature - and can be enabled or disabled for each individual network.
Use private Wi-Fi addresses in iOS 14, iPadOS 14, and watchOS 7 - Apple Support
